A light source device including a light emitting element and a phosphor attracts attention as the next-generation light source device whose low power consumption, reduced size, high luminance, and wide-range color reproducibility are desired, and has been extensively researched and developed. Generally, primary light emitted from the light emitting element has a peak wavelength in a range of a near-ultraviolet region to a blue region. For example, the primary light has peak wavelength in a wavelength region of 380 nm to 490 nm. Light source devices which include various phosphors suitable for respective applications have also been proposed.
For example, a variety of light source devices to be used as a light source of an illumination apparatus have been researched and developed, and a lot of techniques for improving output performance of such a light source device are examined. Generally, a phosphor which has high visibility and has the main emission peak in a complementary color region of the blue (that is, yellow region, green region, or red region) is used for improving output performance of a light source device. It is required that a light source device usable as a light source of general illumination equipment have improved output performance and high color rendering properties (“having high color rendering properties” basically means that an average color rendering index Ra is equal to or greater than 80).
Here, the color rendering index is an index indicating a color shift which occurs when a light source which is a target of measuring the color rendering properties illuminates a color chip for color rendering evaluation. If the color rendering index is high, an occurrence of the color shift is small. That is, a light source which has a high color rendering index and is a measurement target emits light which is able to cause the color of an irradiation target to accurately appear. The color rendering index has R1 to R15 ratings and thus 15 kinds of color chips for color rendering evaluation are provided. The average color rendering index Ra is generally used as an index indicating the color rendering properties, and is an average value of color rendering indices R1 to R8 among color rendering indices R1 to R15.
Measures of improving tone of an irradiation target are provided in order to cause a light source device used as a light source of an illumination apparatus to satisfy the above requirements. For example, International Publication No. 2011/108203 (PTL 1) describes an LED lamp which includes an LED light source and a filter. The LED light source described in PTL 1 includes a blue LED, a green or yellow phosphor, and a red phosphor. The blue LED has the main emission peak in a wavelength region of 440 nm to 460 nm. The green or yellow phosphor is excited by light emitted from the blue LED. The red phosphor is excited by light emitted from at least one of the blue LED and the green or yellow phosphor. The filter described in PTL 1 reduces at least a portion of radiant intensity of light having a wavelength region of 570 nm to 590 nm emitted from the LED light source.
PTL 1 describes that by using the filter that reduces radiant intensity of light having a specific wavelength and the LED light source that includes red phosphor, it is possible to cause a neutral tint in PTL 1, the neutral tint is defined to be test colors of R1 to R8 at middle chroma) and vivid red color to look natural. However, the LED lamp described in PTL 1 includes the filter. Thus, the number of works in a production process of the LED lamp increases and production costs for the LED lamp increases. Since at least a portion of radiant intensity of light having a wavelength region of 570 nm to 590 nm is reduced by the filter, power efficiency of the illumination apparatus is reduced.
International Publication No. 2013/150470 (PTL 2) describes that it is possible to provide “dazzling white” by a light emitting module which includes a light emitting element that emits light having an emission peak in a wavelength region of 400 to 440 nm and a light emitting element that emits light having an emission peak in a wavelength region of 440 to 460 nm. The reason is because the light having an emission peak in a wavelength region of 400 to 440 nm excites a fluorescent agent adhering to clothes and thus blue light is emitted. That is, in a case where clothes or the like is irradiated with output light of the light emitting module in PTL 2, light reflected by the clothes or the like includes a blue-light component stronger than the output light of the light emitting module, and thus is caused to look whiter than the output light of the light emitting module.